Air conditioning systems typically contain an air side loop where the air to be forced into the zone or space being air conditioned is either heated or cooled as desired.
In many modern, industrial type air conditioning systems, the air side of the air conditioning system consists of a central station air handler. A central station air handler is designed to have the flexibility to accommodate the air handling needs of various industrial users by assembling any number of specialized but compatible components in the air handler, each of which have a different function. The requirements vary depending on the application such as, for example, use with a large retail outlet, a hospital, or a light industrial manufacturing plant. Accordingly, a number of different components are designed to be selected and assembled in a single unit as desired for the particular application.
Central station air handling units may include a fan unit, an inspection blank, a coil, a filter, a mixing box and a discharge plenum. Special applications might require additional components. A hospital, for example, may have unique filtering requirements that would require inclusion of a number of different filter units in the air handler.
The various components of a central station air handler are designed to be assembled together into a single unit in which the air flow starts at one end and is discharged at the opposite end. The fan forces air through the coil where the air is cooled or heated. The filter removes certain unwanted materials from the conditioned air. The mixing unit is incorporated in certain applications to mix exterior air with the return air in order to take advantage of the cooling effect of the outside air during the cooler seasons of the year and to provide a certain amount of fresh air to the building so that the various zones do not feel stuffy to the occupants. Finally, the discharge plenum unit accepts the chilled/mixed air and discharges it into the air conditioning ducts for conveyance to the various zones for cooling the zones.
In the case of modular air handlers, the various components of a central station air handler are assembled into a single unit by bolting the internal frame of each component to the internal frame of the adjacent components. The assembly usually is accomplished at the factory so that the air handler is shipped as a specialized unit to the site for installation. A spring loaded suspension system is provided to isolate the air handler's fan from the air handler cabinet and building structure.
In the past, the suspension system for supporting the fan has been designed as an add-on feature mounted beneath the fan or suspended from special brackets. The suspension system designs have typically utilized a coil spring contained between two housings made of a cast metal. An oppositely directed cup is located at either end of the spring to contain the spring. The spring is then held in place between the two cups by the compressive force of the weight of the air handler.
The suspension system was usually procured by the air conditioner manufacturer from a fabricator vendor that produced the suspension systems. In order to mount the suspension system, the manufacturer had to make an upper and a lower suspension system mount that effectively was redundant with the upper and lower housings of the suspension system that was supplied to the manufacturer. Accordingly, the lower housing was affixed to the unit base with bolts mounted to a specially designed mount. Likewise, the upper housing was affixed to the fan with a central bolt to a mount that is specially designed to mate the suspension system to the fan. This means of mounting the suspension system required the production and utilization of redundant mounting devices. Further, suspension systems of this design are susceptible to lateral loads imposed on the air handler. The lateral loads on the air handler have a tendency to dislodge the coil spring from the cups. Extensive time and cost is required to repair a suspension system once the springs have been dislodged.
In order to accommodate lateral loads, later suspension systems were designed with the housings having tongues descend a substantial distance in two opposed quadrants. While such housings can accommodate lateral loads on the air handler in a single direction, the long descending tongues of the upper cup are susceptible to jamming on the lower cup when vertical loads were imposed on the air handler, thereby disabling the suspension system. Additionally, the castings and mounts represent a cost that should be eliminated in the interest of efficiency.
An alternate design includes plates welded on either end of the spring, with one of the plates bolted to the unit base and the other bolted to the fan. While this design deals with the problem of spring dislodgement and jamming due to lateral forces, it resulted in another problem. Since there is no lateral restraint of the springs in this design, the use of such suspension systems made the air handling unit unduly subject to lateral motion. This motion was essentially unchecked and was therefore undesirable. Additionally, the heat generated during welding frequently had the effect of adversely affecting the resilient qualities of the spring. A further problem with this design is that it makes replacement of the spring very difficult since the spring is welded to two mounting plates that are in turn bolted to the building structure and to the rails of the air handler.
Mounting of the suspension system to the air handler should be as simple as possible and redundant parts eliminated. Suspension systems of the types just described frequently required special upswing cantilever brackets at each corner of the air handler from which the suspension system depended. Such brackets were utilized to reduce the vertical height that the suspension system added to the air handler. In these uses the manufacturing costs included not only the separate suspension system, but also included the special cantilever bracket as well.
There is an ancillary need to provide restraint for the air handler in some applications where there is a likelihood of seismic activity. This restraint must permit a certain amount of movement in response to a seismic event while, at the limit of the movement allowed, providing positive restraint of the air handler so that the air handler is not displace from its mounting position in the building during a seismic event. The restraint needs to be in both the horizontal and vertical planes. Snubbers have in the past been added to the air handler for that purpose. Typically, the snubbers were located along the sides of the air handler. Again these were designed by fabricator suppliers and required their own dedicated mounting devices to mount the snubbers both to the building and to the air handler. This also added redundancy in the mounts to the suspension system. It would be a decided advantage to have the seismic snubbers integrated with the suspension system and be of simple design. Redundant mounts must be eliminated.
The industry needs to provide adequate suspension of air handlers with a minimum of cost and a maximum of flexibility with respect to replacing and inter changing the spring component of the suspension system. Accordingly, it would be a decided advantage in the air conditioning industry to provide a suspension system for an air handler that could successfully withstand significant lateral forces on the air handler without dislodging the coil spring, and which could sustain large vertical forces on the air handler without the upper housing of the coil spring becoming compressibly engaged with the lower housing of the coil spring. Further, it would be advantageous to provide a suspension system that is integral to the support rails in order to reduce manufacturing costs and to minimize the height added by the suspension system to the air handler package. Special bracketing to support the suspension system should be minimized.